Diffuse reflectivity meter



` May 30, 1961 s. NEWMAN 2,986,065

DIFFUSE REFLECTIVITY METER 2 Sheets-Sheet l T uzl.

Filed March 29, 1957 May 3o, 1961 DIFFUSE Filed March 29, 1957 S. NEWMANREFLECTIVITY METER 2 Sheets-Sheet 2 United States Patent DIFFUSEREFLECTIVITY METER Sam Newman, 50-14 Broadway, Woodside 77, N.Y.

Filed Mar. 29, 1957, ser. No. 649,579.

4 Claims. (Cl. 88-14) (Granted under Title 35, U.S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to a diliuse reflectivity meter and moreparticularly to a diffuse reflectivity meter that is portable and can bepositioned adjacent any selected area of a surface that is small andsubstantially flatfto meter diffused light emanating from the selectedarea in a direction perpendicular thereto.

Diffuse reflectivity is the ratio of the amount of light dilfuselyscattered from a surface to the amount of light diffusely scattered froma perfectly white surface.

This invention has particular utility in ascertaining somecharacteristics of a dark trace tube screen.l A dark trace tube is acathode ray tube with a light absorbing screen, a scotophor, rather thana light emitting screen, a phosphor, as in conventional cathode raytubes. The screen material o-f a dark trace tube is an alkali halide;potassium chloride is commonly used as the screen material. Whenelectrons with an energy on the order of ten kilovolts collide with thescreen, color centers or F-centers are formed in the crystalline matrixof the screen material. The color centers or F-centers absorb light inthe yellow-green region of the spectrum whereby there appears a magentacoloration. Since light reaching the dark trace tube screen is dividedinto one part that passes through, a second part that is absorbed by thescreen, and a third part that is diifused, the dilfuse reectivity of thescreen is changed with the creation of color centers in the screenbecause more light is labsorbed and less is diffused. The extent of thechange of diffuse reectivity is a function of the density of colorcenters. This invention is adapted to measure diffuse reectivity of adark trace tube screen for any color center density.

Several significant screen characteristics are ascertainable from dilusereflectivity measurements. First, there is signal contrast on the screenwhich is the percent change in diffuse reflectivity of the screenmaterial caused by the incident electron beam as compared to the blankscreen or before the display of a signal. Then there are tonal range,signal buildup by either continuous or pulsed bombardment, erasurespeed, comparison of focus on-center and oit-center, and rate of decayall of which are ascertainable from diffuse reliectivity measurements.

This invention also has utility for ascertaining the correspondingcharacteristics of black-and-white and color tubes, particularly decay,and also the diffuse reilectivity of reflectors.

Briefly, the invention includes a black serrated tube adapted to bepositioned perpendicular to and a short distance from a preselected areaof a test surface. Several conventional light bulbs are supported aroundthe tube. A rheostat is connected in series with the bulbs and thecombination of rheostat and bulbs is adapted to be connected to anddisconnected from a suitable power fice supply by a switch. A meter isadapted to indicateA the voltage across the bulbs whereby the luminousllux emitted by the bulbs may be set to a desired levelbyl.`

Because the same meter isf photomultiplier and the end of the black tubetorender s the-sensiivityrof the photomultiplier as much like the eyeasl possible- The length of the black tube, the distance between one endthereof and the photomultiplier, kandfthe distance .between theother'endfof the tube and the diffusing surface is set so as to focustheselected areaof diffusing surface on the cathode of the-photomultiplier.A sighting VVarrangement is provided forobtaining proper alignment ofblack tube and the selected 'area of diffusing` surface. A differentialamplifier is connected to the output ofthe photomultiplier. The meter isadapted to be connected to the output of the differential ampliiier bymeans of the double-pole double-throw switch. The differential ampliiierincludes a Zero adjustment for dark current. Thephotomultiplier'vcircuit includes a gain control which is set till fullscale deection is obtained on the meter when the selected surface areais white or is otherwise the standard for comparison. The entireinvention ismounted on an adjustable tripod; the platform of the tripodis tiltable in any direction.

An object of this invention is to provide a diffuse reflectivity meter.f f A further object is Vto provide a diffuse `reflectivit meterparticularly adapted to taking measurements on dark trace tube screens.l

*A further object is to provide aV diffuserreflectivity meter that 4isadjustableportable, compact and easy yto use both in the laboratory andin the ield. 'Av further object is to provide a dilfuse rellectivitymeter thatalso can measure transmittance.

A further object is to provide a difluse reectivity meter that may beused at various light levels and whose operation is simple,trouble-free, and stable.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l is front View of the invention, v Fig. 2 is side sectional'vew ofthe invention showing only those elements necessary for explaining theinven-I tion, circuit elements, knobs, meter, and fastenings 'be'-tiltable. A housing 14 open on side 16 is secured on ther platform ofthe tripod 12. A chassis 18 is mounted in the housing. On the chassis 18is mounted a black lightsealed can 22. Within the can, a photomultiplier24 is rigidly mounted. A black tube 26 that is internally serrated alongits entire length is Supported at one end thereof by the can 22 inalignment with the cathode of photomultiplier 2'4. Suitable lightsealing means 28 such as a black rubber grommet engages the tube 26 inthe opening of the can 22. Tube 26 is further supported by a member 34which is secured to housing 14. A photopic ilter 36 is supported betweenthe end of tube 26Y and the photomultiplier 24 to correct the spectralresponse of the photomultiplier 24 to simulate the response of the humaneye. A plurality of lights 38 are mounted around the tube 26. The top ofhousing 14 is formed with a slot 42 which permits air circulation. Afiducial mark 44 is formed adjacent the slot 42. An adjustable membersuch as a screw threadedly engages the tube 26 and extends verticallytherefrom. The screw 46 is adapted to be secured by a locknut 48. Theopen end of the housing is adapted to abut the surface under test, e.g.,the face of the dark trace tube.

To design an embodiment of the above-described combination, the area ofthe target is selected. The smallest photomultiplier practical for theconditions is selected. The useful area of the photomultiplier cathode,which is considerably less than total cathode area, is ascertained fromavailable literature. The area of the target and the useful area of thecathode on which it is to be focussed is established. The nextconsideration is that the distance between target area and cathodeshould be mini'- mal. circuit and structural elements, the distance neednot be smaller than the distance made available by the housing 14.Having established the distance, it is necessary to design a focusdevice for focussing light rays that leave the target in a directionnormal and substantially normal thereto. Though a lens system could beused it would be expensive and not sufliciently rugged. Instead a blacktube is mounted between the target area and the cathode for focussing.From established principles of optics the relationship of insidediameter and length of tube 26, the space between one end thereof andthe cathode of the photomultiplier and the other end thereof and thetarget area all may be calculated to focus the target area on thecathode. Any one of many designs can satisfy the focus requirements; noone dimension is critical. As a matter of fact the proper combination ofvariables can be arrived at empirically by changing one or two of thevariables to fixed quantities and changing the remaining variables untilfocus is established. It is to be noted that the spacing between thetarget area and the end of tube 26 is adequate to permit the bulbs 38 toilluminate the target area. The bulbs 38 are small, preferably six voltbulbs. A sighting arrangement is provided similar to that on a rifle forenabling alignment of the tube 26 with the target area. The sightingarrangement includes the head of screw 46 and the mark 44. When the mark44 and the head of screw 44 are in line with the center of the targetarea the tube 26 is aligned with the target area. The serrations in thetube 26 attenuate and substantially eliminate side effects, that is,rays of light that do not enter tube 26 parallel to the axis thereof.

The circuit diagram of the meter shown in Fig. 3 designates theparameters for one particular embodiment built and used and found to besatisfactory. The designation of parameters is not intended in alimiting sense.

The several bulbs 38 are connected in series with each other and with alight adjusting rheostat 52 and a fuse 54 anda switch 56; the bulbcircuit is adapted to be connected to a suitable power supply. Abattery, not shown, is included as the lamp power supply to permit usein the field. Otherwise connection may be made to a direct current oralternating current line. A direct current voltmeter is adapted to beconnected across the bulbs 38. Where the power supply for the bulbs 38is A.C. there is provided a meter rectifier 62. Where the power supplywill be D.C. the meter rectifier is omitted. A meter resistor 64 isprovided whereby the voltage range of the meter will include the rangeof voltage across the bulbs 38 and the scale of the meter is properlycorrelated with voltage across the bulbs 38. The meter terminals areconnected to the contactors of a double-pole doublethrow switch 66. Whenthe contactors of the doublepole double-throw switch engage the lowercontacts, the meter 58 indicates the voltage across the bulbs. Therheostat 52 is adjusted so that voltage across the bulbs However, sincethe housing 14 supports various is equal to a predetermined amount. Thevoltage across the bulbs is measured to establish the desired lightoutput of the bulbs.

A low-current high voltage direct current power supply 72 is providedfor the photomultiplier 24. The positive terminal of the power supply 72is connected to a source of reference hereinafter referred to as ground.A gain control rheostat 74 is connected between the cathode and thenegative terminal of the power supply 72. A voltage divider including aseries of resistors 76 is connected at one end to the cathode of thephotomultiplier and to the plurality of dynodes in succession. Aresistor 78 is connected at one end to the dynode closest to the` plate.A switch 82 is connected between the other end of resistor 78 andground. The plate of the photomultiplier 24 is connected to groundthrough a grid input resistor 84. The input grid of a differentialamplifier is connected to the grid input resistor 84 of a differentialamplifier 86. The differential amplifier is conventional and detaileddescription thereof is deemed unnecessary. The amplifier utilizes doubletriodes because higher transconductance is obtained thereby. Theamplifier includes a zero adjustl potentiometer 88. A power supply 92 isprovided for the differential amplifier. The negative ter minal of powersupply 92 is grounded. A switch 94 is connected between the positiveterminal of power supply 92 and the tap of the zero adjust potentiometer88.

`The switches 82 and 94 are ganged so that the circuit may bedeenergized conveniently.

The output terminals of amplifier 86, that is, the plates of therespective tubes thereof, are connected to the other two terminals ofthe double-pole double-throw switch 66. When the contactors of theswitch 66 engage the upper contactors, the meter 58 indicates the outputof the photomultiplier.

A jack socket for a recorder is indicated at 96. When a jack, not shown,is inserted, the amplifier 86 is disconnected from power supply 92; alsothe plate of the photomultiplier is connected through the recorder toground. This arrangement is indicated so that a commercial recorder maybe plugged in to record the output of the photomultiplier. The amplifieris deactivated as explained above when the recorder plug is insertedinto the jack socket.

In utilizing the invention to measure diffuse refiectivity ofthe face ofa dark trace tube it is necessary first to adjust the circuits of thedark trace tube being tested. The deflection circuits are adjusted untila raster of the required area and in the desired position is written onthe face of the tube. This may take a little time since the propersetting of the deflection circuits is arrived at by trial and error andsince the tube face must be erased after each try. Then the desired beamcurrent is established. The various electrode voltages established atpreselected levels and maintained at those levels except for one of theelectrodes whose potential is made such that the beam is normallycutoff; the one electrode is adapted to be pulsed so that the beamcurrent is turned on during the pulse interval and for one or morecomplete frames. All these preliminary settings are necessary since thecoloration, the diffuse reflectivity and the absorptivity of the screenare functions of color center density, and color center density isaffected by each of the aforementioned variables. The scotophor storesthe image for hours without appreciable decay. The charge density of thepulsed raster is therefore dependent on the following factors:

The area of the raster The duration of time the pulse is written Thebeam current of the dark trace C.R.T.

The focussing of the beam The location of the raster on the face of thedark trace C.R.T.

After the dark trace tube circuitry is set, the tripod 12 is positionedso that the open end of the housing 14 abuts the face of the dark tracetube. A raster is written by the preset circuitry as an aid in adjustingthe tripod 12. The platform of tripod 12 is adjusted until the mark 44and the head of screw 46 is in line with the center of the raster andthe open end of housing 14 abuts the face of the dark trace tube. Thenthe tube 26 is in line with the raster or target area. Then the rasteris erased. 'I'he light switch 56 is turned on and the meter switch 66 ismoved to the position for indicating voltage across the lights. Therhcostat 52 is adjusted until the voltage across the lights is at thepredetermined level. Then the light switch 56 is moved to off and themeter switch 66 is thrown to output position and the ganged switches 82and 94 are moved to on position. The recorder mentioned above is notconnected to the circuit at this time. The zero adjust potentiometer 88is adjusted until the meter deflection is zero. Then the light switch 56is turned on and the gain rheostat 74 is adjusted until the meterdeection is one hundred percent. The dark trace tube is pulsed to writea raster of one or more frames. Neglecting the transistoryphosphorescence during the interval the pulse is written, the meterindicates the diiuse reflectivity as a percentage of the diffusereiiectivity before the raster was written. To obtain a recording oftonal range, buildup, decay, erasure speed and other characteristics ofthe screen material,

6 I claim: 1. A diiuse reflectivity meter comprising support means, aphototube mounted on said support means, an internally serrated blacktube mounted on said support means in line with the useful area of thecathode of said Y cluding a zero adjust means connected to saidphototube,

the recorder is plugged in and thereby substituted for the amplifier andmeter circuit. The recorder is adjusted for zero and one hundred percentdeliection in the same way described above for the meter.

This invention has been described in connection with dark trace tubes,actually it has many other uses. Some of these are the measurements ofphosphor characteristics of bright trace tubes, such as P7 and P11. Thedecay of a bright trace tube can be measured by adjusting the recorderfor 100% when the tube is at maximum brightness and zero percent whenthe C.R.T. is cut oli. Measurements of contrast, intensity, andliuorescence can be measured. O-ther applications where light reectiveor transmitting surfaces are used can be measured by comparison to astandard sunface or by comparison to similar surface. Examples aresurfaces of lighting projectors, matte diffusing surfaces, points,colored surfaces, clear and opalescent surfaces, and translucent glassesor plastics.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is thereore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

meter means adapted to Ibe connected across said lighting means toindicate the voltage thereacross and also adapted to be connected to theoutput of said amplifier means whereby the voltage output of saidamplier means may be indicated.

2. A diffuse reflectivity meter as defined in claim l further includinga photopic filter disposed between said phototube and said yblack tubeto cause the spectral response of said phototube to approximate that ofthe human eye.

3. A diffuse reectivity meter as defined in claim 1 wherein said supportmeans is a box with one open side and said black tube is normal to theopen side of said box and terminates short of the open side, the openside of said box being adapted to be placed approximately against asurface whose diiiuse reiiectivity characteristics are to beascertained.

4. A diuse reliectivity meter as defined in claim 3 wherein the top ofsaid box near the side opposite the open side is formed with an opening,a iiducial mark on said box adjacent the opening, a raised elementsecured to the upper end portion of said black tube nearest the openside of said Ibox whereby said Iblack tube is aligned with a selectedarea of said surface when said ducial mark and said raised element andthe center of said area are in line.

References Cited in the tile of this patent UNITED STATES PATENTS1,794,134 Baker et al. Feb. 24, 1931 2,165,054 Johnson July 4, 19392,542,299 Archer et al Feb. 20,1951 2,632,358 Ehat Mar. 24, 19532,710,924 Morrisonet al June 14, 1955 2,797,334 Sweet .Tune 25, 19572,852,693 Hughes et al. Sept. 16, 1958 FOREIGN PATENTS 530,724 GreatBritain Dec. 18, 1940

